Process for producing an acetal

ABSTRACT

An acetal is produced at a high yield and a high selectivity by contacting an olefin and an alcohol with each other in the presence of (a) a nitrite, (b) a platinum group metal or the salts thereof and (c) a halide at a high reaction rate without requirement of any troublesome operations for the separation, recovery and regeneration of the catalyst.

This is a continuation of application Ser. No. 333,110 filed Dec. 21,1981, and now abandoned.

The present invention relates to a process for producing an acetal and,more specifically, it relates to a process for producing an acetal froman olefin and an alcohol.

Acetals can be applied in various ways industrially as startingmaterials for the synthesis of organic solvents, perfumes andagricultural chemicals, and can be converted to vinyl ether, which is astarting material for producing water-soluble polymers by the removal ofalcohol, and the like.

Heretofore, acetals have been industrially produced by, for example, thereaction of an alcohol with an aldehyde or the oxidation of an alcoholwith manganese dioxide and sulfuric acid.

Also known in the art are various methods for producing acetals byreacting olefins, alcohols and oxygen in the presence of platinum metalcatalysts.

However, the above-mentioned methods for the production of acetalspresent problems from an industrial point of view in that the reactionrate is low. The yield of and the selectivity to the desired productsare not good, and the catalyst systems are complicated, and theoperations for the separation, recovery and regeneration thereof aretroublesome. Therefore, these methods have not yet been used as anindustrial process.

Accordingly, an object of the present invention is to obviate theabove-mentioned problems concerning the prior methods for producing anacetal and to provide a process for producing an acetal from an olefinand an alcohol.

Another object of the present invention is to provide a process forproducing, at a high yield and a high selectivity, an acetal from anolefin and an alcohol at a high reaction rate without the requirement ofany troublesome operations for the separation, recovery and regenerationof the catalyst.

Other objects and advantages of the present invention will be apparentfrom the following description.

In accordance with the present invention, there is provided a processfor producing an acetal comprising the step of contacting an olefin andan alcohol with each other in the presence of (a) a nitrite (i.e. anester of nitrous acid), (b) at least one component selected from thegroup consisting of platinum group metals and the salts thereof and (c)at least one halide (or halogenide).

Typical examples of olefins used as a starting material in the presentinvention are: aliphatic olefins such as ethylene, propylene, butene,isobutylene and the like; olefin aldehydes such as acrolein,crotonaldehyde and the like; olefin ketones such as methyl vinyl ketone,ethylidene acetone, allyl methyl ketone and the like; olefin nitrilessuch as acrylonitrile, methacrylonitrile, crotononitrile and the like;olefin carboxylic acids and the esters thereof such as acrylic acid,methacrylic acid, crotonic acid, cinnamic acid and the like; olefinamides such as acrylamide, methacrylamide and the like; alicyclicolefins such as cyclopentene, cyclohexene, cycloheptene and the like;and styrene.

Typical examples of alcohols also used as a starting material in thepresent invention are aliphatic alcohols having 1 to 12 carbon atomssuch as methanol, ethanol, n-or i-propanol, n-or i-butanol, sec-butanol,n-or i-heptanol, n-or i-octanol, n-or i-decanol, n- or i-dodecanol andthe like. These alcohols may be substituted with any substituents suchas an alkoxyl group, a halogen atom, a phenyl group and the like as longas these substituents do not adversely affect the desired reaction.

Typical examples of nitrites also used in the present invention arethose derived from the above-mentioned alcohols and nitrous acid. Suchexamples are methyl nitrite, ethyl nitrite, propyl nitrite, butylnitrite, amyl nitrite, hexyl nitrite, heptyl nitrite, nonyl nitrite,decyl nitrite, tridecyl nitrite, hexadecyl nitrite, benzyl nitrite andthe like.

These nitrites can be generally used in an amount of 0.01% by weight ormore, preferably 0.1% through 20% by weight, based on the amount of thestarting alcohol in the case where the reaction is carried out in aliquid phase. In the case where the amount of the nitrites is less than0.01% by weight, the production yield and the production rate of thedesired acetal tend to be decreased.

In the case where the reaction is carried out in a vapor phase, theratio of the olefins, the alcohols and the nitrites in the vapor phaseis approximately 5-25% by volume: 5-25% by volume: 1-30% by volume,although the ratio can vary widely.

The nitrites can be previously charged into a reaction system, or can beintroduced into a reaction system in such a form that the nitrites arediluted with an inert gas such as nitrogen gas, carbon dioxide gas orthe like, in the case where the reaction is carried out in a liquidphase. In the case where the reaction is carried out in a vapor phase,the nitrites can be charged alone into a reaction system or can becharged into a reaction system in a mixture with the olefins and/or thealcohols and, generally, can be charged into a reaction system in such aform that the nitrites are diluted with an inert gas, such as, nitrogengas, carbon dioxide gas or the like.

Instead of the nitrites, nitrogen oxides or the hydrates thereof can becharged, optionally together with oxygen, into a reaction system,whereby the nitrites can be formed by the reaction thereof with thealcohols in the reaction system.

The platinum group metals and the salts thereof used as a catalyst inthe present invention include, for example, palladium, platinum,rhodium, ruthenium iridium and osmium and the halides, sulfates,nitrates, phosphates and acetates thereof. These catalysts can be used,together with an adequate amount of other metals such as gold, vanadium,molybdenum and the salts thereof.

The catalysts can be used in a concentration of 1 ppm through 10% byweight, preferably 100 through 1000 ppm, in terms of the platinum metal,in the reaction liquid in the case where the reaction is carried out ina liquid phase.

In carrying out the present invention, the catalysts can be desirablysupported, together with the co-catalysts mentioned below, on a suitablecarrier such as activated carbon, silica gel, alumina, silica-alumina,silicon carbide, diatomaceous earth, magnesia, pumice stone, molecularsieves and the like, in order to facilitate the recovery of thecatalysts and/or the desired products from the reaction mixture and alsoto prevent the loss of the catalysts. Although there is no criticallimitation regarding the amount of the catalyst supported on thecarrier, the amount of the catalyst, in terms of platinum group metal,is desirably 0.01% by weight or more and, more desirably, 0.1 through1.0% by weight, based on the weight of the carrier.

The halides (or halogenides) used as a co-catalyst in the presentinvention can be any compounds which contain halogen atoms (i.e. F, Cl,Br, I). Typical examples of the halides which can be desirably used inthe present invention are: hydrogen halides; the halides of platinummetals such as palladium, platinum, rhodium, and iridium; the halides ofalkali metals such as sodium, potassium and lithium; the halides ofalkaline earth metals such as calcium and magnesium; the halides ofcopper such as copper chlorides, copper bromides an copper iodides; thehalides of iron such as FeCl₂, FeCl₃, FeCl₂.4H₂ O, FeCl₃.6H₂ O and FeBr₃; and the halides of the other metals or non-metals such as cobalt,zinc, nickel, aluminum, molibdenum tin, manganese, chronium, antimonyand the like.

These halides can be desirably used in an amount of 0.1 through 10, moredesirably 0.5 through 5, and, most desirably, 0.5 through 2, in terms ofan atomic number of a halogene atom, based on the platinum group metal,in view of the increasein the yield of and the selectivity to thedesired product. In the case where the halide of the platinum metal isused as the catalyst in the present invention, the halide is notnecessarily present in the reaction mixture.

In the case where the present reaction is carried out in a vapor phase,iron compounds, other than the halides of iron, such as Fe₂ O₃, Fe₃ O₄,Fe(OH)₃, FeCO₃, Fe₂ (SO₄)₃ and Fe(NO₃)₃.9H₂ O can be desirably used, inaddition to the above-mentioned halides. The amount of the ironcompounds is 0.1 through 10, desirably 0.5 through 5, in terms of anatomic number of an iron metal, based on the platinum group metal.

The reaction can be carried out in the presence of, or in the absenceof, an inert solvent. Examples of such inert solvents are: the esters oflower fatty acids such as ethyl acetate, propyl acetate, butyl acetate,amyl acetate, ethyl propionate, butyl propionate, methyl lactate, ethyllactate, propyl lactate, butyl lactate and the like; the esters ofaliphatic dicarboxylic acid such as dimethyl oxalate, diethyl oxalate,dipropyl oxalate, dibutyl oxalate, dimethyl succinate, diethylsuccinate, dimethyl adipate and the like; carbonic acid diesters such asdimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutylcarbonate and the like; the esters of aromatic carboxylic acids such asmethyl benzoate, ethyl benzoate, dimethyl phthalate and the like; etherssuch as dioxane, dibutyl ether and the like; hydrocarbons such asbenzene, toluene, xylene, cyclohexane, n-hexane and the like; and theother solvent such as monochlorobenzene, dichlorobenzene, nitrobenzene,acetophenone, alkylsulfone, alkylsulfoxide and the like.

Furthermore, the production rate of the acetal can be further increasedby the addition of oxygen in an amount of, for example, 0.1 through 10%by volume in a feed gas. In the case where, as mentioned hereinabove,the reaction is carried out, while introducing the nitrites into areaction vessel, the oxygen can be introduced as a mixture thereof withthe nitrites.

The present invention can be desirably carried out in a liquid phase ata temperature of 20° through 150° C. under an atmospheric pressure orunder pressure, for example, up to 200 kg/cm² G.

The present reaction can be desirably carried out at a temperature of50° through 200° C. under an atmospheric pressure or under pressure, forexample, up to 20 kg/cm² G, in the case where the reaction is carriedout in a vapor phase. The starting gaseous materials can be desirablycontacted with a catalyst layer or bed at a space velocity (S.V.) of 500through 5000/Hr.

The present invention will now be further illustrated, but is by nomeans limited to, the following Examples and comparative Examples.

EXAMPLE 1

Into a four-necked flask provided with a gas feed pipe, an olefin feedpipe, a thermometer and a reflux condenser, 50 ml of n-butanol and 0.1 gof palladium chloride were charged. The contents in the flask weremaintained at a temperature of approximately 86° C. 5.3 g ofacrylonitrile was added to the flask with stirring over 50 minutes,while a nitrogen gas containing 12% by volume of n-butyl nitrite wasintroduced into the flask at a rate of 210 ml/min. over 60 minutes. Theeffluent gas discharged from the top of the reflux condenser wasintroduced into a trap containing 50 ml of n-butanol, which was cooledby a dry ice-methanol bath, whereby the reaction products werecollected.

The reaction products in the flask and the butanol trap were analyzed bymeans of gas chromatography. As a result, 27.4 m mol ofcyanoacetaldehyde di n-butylacetal was produced and, as a by-product,only trace amounts of C₄ H₉ OCH═CHCN were formed.

EXAMPLES 2-5

Reactions were carried out in a manner as described in Example 1, exceptthat the liquid composition at the beginning of the reaction, and thefeed rate of nitrogen gas containing n-butyl nitrite were changed asshown in Table 1 below.

The results thus obtained are shown, together with results in Example 1,in Table 1 below.

                  TABLE 1                                                         ______________________________________                                             Feed Rate of                                                                              Liquid Composition                                                                          Yield of                                            Nitrogen Gas                                                                              at Beginning of                                                                             Cyanoacetaldehyde                              Ex-  Containing  Reaction (ml) Di n-Butyl-                                    am-  n-Butyl Nitrite                                                                           n-Butyl         Acetal                                       ple  (ml/min.)   Nitrite n-Butanol                                                                             (m mol)                                      ______________________________________                                        1    210          0      50      27.5                                         2    "           10      40      39.0                                         3    100          0      50      15.8                                         4    "           10      40      25.8                                         5    None        "       "       15.2                                         ______________________________________                                    

EXAMPLE 6

Into a flask provided with an agitator, 1400 ml of methanol, 600 ml ofacrylonitrile and 1.2 g of palladium chloride were charged and thecontents in the flask were maintained at a temperature of 63° C. 220l/hr of a circulating gas was continously charged into the flask withstirring. Said circulating gas was obtained by passing a gas dischargedfrom the outlet of the flask, together with 7-8 l/hr of oxygen, througha methanol liquid, and contained 44% by volume of methyl nitrite and 45%by volume of nitrogen monoxide.

As a result, the space time yield of cyanoacetaldehyde dimethylacetalwas 25 g/l.hr at 6 hours after the beginning of the reaction.

EXAMPLE 7

The reaction was carried out in a manner as described in Example 3,except that air containing 12% by volume of n-butyl nitrite was fed at arate of 100 ml/min. in lieu of the nitrogen gas containing 12% by volumeof n-butyl nitrite.

As a result, 46.3 m mol of cyanoacetaldehyde di n-butylacetal wasformed.

COMPARATIVE EXAMPLE 1

The reaction was carried out in a manner as described in Example 3,except that air was fed into a flask at a rate of 90 ml/min. in lieu ofthe nitrogen gas containing 12% by volume of n-butyl nitrite.

As a result, no formation of acetal was observed.

EXAMPLES 8-13 AND COMPARATIVE EXAMPLES 2-5

Into the four-necked flask used in Example 1, 20 ml of methanol, 10 mlof methyl acrylate, 50 ml of 1,4-dioxane (i.e. solvent) and the givenamount of a catalyst as listed in Table 2 below were charged.

Then, the contents in the flask were maintained at a temperature ofapproximately 63° C. and, with stirring, air, or air containing, 13% byvolume of methyl nitrite, was fed into the flask for 30 minutes at arate of 100 ml/min.

The results are shown in Table 2 below.

                                      TABLE 2                                     __________________________________________________________________________                               Yield of Formylacetic                                      Catalyst        Feed                                                                             Acid Dimethylacetal                                No.     (m mol)         Gas                                                                              (m mol)                                            __________________________________________________________________________    Example                                                                        8      PdCl.sub.2 (0.56)                                                                             Air*                                                                             11.5                                                9      PdCl.sub.2 (0.56) + CuCl.sub.2 (3.72)                                                         "  8.0                                                10      10 wt % Pd/C (0.56) + CuCl.sub.2 (3.72)                                                       "  9.1                                                11      10 wt % Pd/C (0.56) + CuCl.sub.2 (0.56)                                                       "  9.3                                                12      10 wt % Pd/C (0.56) + SnCl.sub.4 (0.46)                                                       "  9.6                                                13      10 wt % Pd/C (0.56) + FeCl.sub.3 (1.12)                                                       "  7.8                                                Comparative                                                                   Example                                                                        2      PdCl.sub.2 (0.56) + CuCl.sub.2 (3.72)                                                         Air                                                                              2.6                                                 3      PdCl.sub.2 (0.56) + CuCl.sub.2 (3.72) +                                                       "  1.1                                                        Et N.sub.3 (4.26)                                                      4      10 wt % Pd/C (0.56)                                                                           Air*                                                                             0                                                   5      Pd (OAC).sub.2 (0.56)                                                                         "  0                                                  __________________________________________________________________________     *Containing 13% by volume of methylnitrite                               

EXAMPLES 14-18

Into the four-necked flask used in Example 1, 50 ml of methanol, a givenamount of an olefin and 0.1 g of palladium chloride were added. Thecontents in the flask were maintained at the temperature listed in Table3 below (i.e. the reaction temperature) and a nitrogen gas containing 8%by volume of methyl nitrite was fed into the flask at a rate of 200ml/min. for the time shown in Table 3 below (i.e. the reaction time).

                                      TABLE 3                                     __________________________________________________________________________         Olefins    Temperature                                                                          Reaction                                                                            Formed Acetal                                    Example                                                                            (m mol)    (°C.)                                                                         Time (hr)                                                                           (m mol)                                          __________________________________________________________________________    14   Cyclohexene                                                                              60     2     1,1-dimethoxycyclohexane                              (100)                   (8.9)                                            15   Methyl Crotonate                                                                         "      3     Methyl β,β-dimethoxy                        (64)                    n-butyrate                                                                    (15.2)                                           16   Methyl Methacrylate                                                                      "      "     Methyl α-metyl-β,β-                   (150)                   dimethoxy propionate                                                          (10.4)                                           17   Methacrylonitrile                                                                        50     4     α-methyl-β,β-                         (120)                   dimethoxy propionitrile                                                       (17.2)                                           18   Methyl Vinyl Ketone                                                                      60     3     4,4-dimethoxy-2-                                      (150)                   butanone                                                                      (12.1)                                           __________________________________________________________________________

EXAMPLE 19

A glass reaction tube having an inner diameter of 25 mm and a length of400 mm was packed with 14.5 g (15 ml) of cylindrical PdCl₂ -CuCl₂ -γ-Al₂O₃ catalysts containing 1.0% by weight of Pd and 1.2% by weight of Cusupported thereon and, further, glass Raschig rings having a diameter of3 mm were packed on the catalyst layer at a height of 120 mm. Thisreaction tube was vertically installed and a ring-type electric oven wasmounted on the outside of the reaction tube. Thus, the temperature ofthe inner catalyst layer was maintained at 80° C. Methyl nitrite dilutedwith nitrogen to a given concentration was fed into the reaction tubefrom the top thereof, and methanol was fed into the reaction tube fromthe top thereof by means of a constant rate pump. On the other hand,acrylonitrile was fed into the reaction tube in the form of a vapor froman evaporator in which the acrylonitrile was heated in a constanttemperature bath having a temperature of 40° C., together with nitrogen.

The result is shown in Table 4 below.

EXAMPLES 20-23

The reactions were carried out in a manner as described in Example 19,except that the kinds of the catalysts, the reaction temperatures, thecompositions of the starting gases, and the space velocities werechanged as shown in Table 4 below.

The results are shown in Table 4 below.

COMPARATIVE EXAMPLE 6

The reaction was carried out in a manner as described in Example 19,except that methanol was not used.

The result is shown in Table 4 below.

                                      TABLE 4                                     __________________________________________________________________________                                                         Space Time                                                    Composition of Starting                                                                       Yield of Cyanoacet-              Catalyst        Reaction     (Vol %)*        aldehyde Dimethyl                (Wt % in terms) Temp Space Velocity Methyl   Acetal                   No.     of Metal)       (°C.)                                                                       (hr)    Acrylonitrile                                                                        Nitrite                                                                           Methanol                                                                           (g/cat · l                                                           · hr)           __________________________________________________________________________    Example 19                                                                            (1% Pd + 1.2% Cu)--Al.sub.2 O.sub.3                                                           80   1330    29.8   17.2                                                                              18.4 23.2                     Example 20                                                                              "             82   1160    12.9   "   "    14.9                     Example 21                                                                              "             "    1550    18.4   "   9.2  16.2                     Example 22                                                                            (2% Pd + 1.2% Cu)--SiO.sub.2                                                                  104  1330    23.8   14.0                                                                              18.4 24.8                     Example 23                                                                            (5% Pd + 1.2% Cu)--SiO.sub.2                                                                  110  "       "      "   "    31.4                     Comparative                                                                           (1% Pd + 1.2% Cu)--Al.sub.2 O.sub.3                                                           80   "       "      15.5                                                                              0    3.4                      Example 6                                                                     __________________________________________________________________________     *Balance of nitrogen gas was contained.                                  

EXAMPLE 24

The reaction was carried out in a manner as described in Example 19,except that ethylene was used in lieu of acrylonitrile, the spacevelocity of the starting gas (ethylene . . . 16.7% by volume, methylnitrite . . . 14.5% by volume, methanol . . . 18.4% by volume, nitrogengas . . . balance) was changed to 930 hr⁻¹, and the reaction temperaturewas changed to 90° C.

As a result, acetaldehyde dimethylacetal was obtained at a space timeyield of 93.1 g/Cat.l.hr.

EXAMPLE 25

A glass reaction tube having an inner diameter of 25 mm and a length of400 mm was packed with 14.8 g (15 ml) of a cylindrical PdCl₂ -FeCl₃/SiO₂ catalyst containing 1.0% by weight of Pd and 1.2% by weight of Feand having a diameter of 3 mm and a height of 3 mm and, further, withglass Raschig rings having a diameter of 3 mm on the catalyst layer at apacking height of 120 mm. The reaction tube was vertically installed anda ring-type electric oven was mounted on the outside of the reactiontube. Thus, the temperature of the catalyst layer was heated toapproximately 80° C.

From the top of the reaction tube, a starting gas mixture containing 18%by volume of ethylene, 14% by volume of methyl nitrite, 14% by volume ofoxygen, 15% by volume of nitrogen monoxide and 39% by volume of nitrogenwas fed into the reaction tube at a rate of 20.4 l/hr and liquidmethanol was fed at a rate of 9 ml/hr (space velocity=1690/hr). Thus,the reaction was carried out at a temperature of 110° C.

After the reaction tube effluent gas was passed through cooled methanol,the effluent gas was passed through a trap in the constant temperaturebath cooled by dry ice-methanol, whereby the reaction products werecollected. The collected liquid was analyzed by means of gaschromatography. As a result, the space time yield of acetaldehydedimethylacetal was 124 g/l.Cat.hr.

EXAMPLES 26-35

The reaction was carried out in a manner as described in Example 25,except that the kinds of catalysts, the reaction temperature, thecomposition of the starting gas, and the space velocity were changed asshown in Table 5 below.

The result is shown in Table 5 below.

EXAMPLE 36

The reaction was carried out in a manner as described in Example 25,except that, from the top of the reaction tube, a starting gas mixturecomprising 15% by volume of ethylene, 10% by volume of methyl nitrite,18% by volume of nitrogen monoxide, and 47% by volume of nitrogen wasfed at a rate of 43 l/hr and liquid methanol was fed at a rate of 9ml/hr (space velocity=3200/hr) and the reaction temperature was changedto 155° C. The result is shown in Table 5 below.

                                      TABLE 5                                     __________________________________________________________________________                                 Space Time Yield                                      Catalyst    Reaction                                                                             Space                                                                              of Acetaldehyde                                       (Wt % in terms                                                                            Temperature                                                                          Velocity                                                                           Dimethylacetal                                   Example                                                                            of Metal)   (°C.)                                                                         (hr.sup.-1)                                                                        (g/l · Cat · hr)               __________________________________________________________________________    25   (1%) PdCl.sub.2 --(1.2%)                                                                  110    1690 124                                                   FeCl.sub.3 /SiO.sub.2                                                    26   (1%) PdCl.sub.2 --(1.2%)                                                                   85    "    87                                                    FeCl.sub.3 /SiO.sub.2                                                    27   (1%) Pd(CH.sub.3 COO).sub.2 --                                                            "      "      15.4                                                (1.2%) Fe.sub.3 (CH.sub.3 COO).sub.9 --                                       (2%) SnCl.sub.4 /SiO.sub.2                                               28   (1%) Pd(NO.sub.3).sub.2 --                                                                105    "    105                                                   (1.2%) FeCl.sub.3 /SiO.sub.2                                             29   (1%) Pd(CH.sub.3 COO).sub.2 --                                                            "      "    95                                                    (1.2%) FeCl.sub.3 /SiO.sub.2                                              30* (1%) Pd°--(1.2%)                                                                   103    "    90                                                    Fe(OH).sub.3 /SiO.sub.2 --HCl                                            31   (2%) Pd°--(1%)                                                                      95    "    45                                                    Fe(NO.sub.3).sub.2 .9H.sub.2 O--(1%)                                          NiCl.sub.2 /Al.sub.2 O.sub.3                                              32* (1%) Pd°--(1.5%)                                                                   101    "    82                                                    Fe.sub.2 O.sub.3 /SiO.sub.2 --HCl                                        33   (1%) PdCl.sub.2 --(1.2%)                                                                  107    "    110                                                   FeCl.sub.3 /Al.sub.2 O.sub.3                                             34   (1%) PdCl.sub.2 --(1.2%)                                                                  105    3200 154                                                   FeCl.sub.3 /SiO.sub.2                                                    35   (1%) PdCl.sub.2 --(1.2%)                                                                  113    1050 97                                                    FeCl.sub.3 /SiO.sub.2                                                    36   (1%) PdCl.sub.2 --(1.2%)                                                                  155    3200 164                                                   FeCl.sub.3 /SiO.sub.2                                                    __________________________________________________________________________     *HCl used was 50 Vol % HCl diluted with N and fed at a rate of 1 ml/min.      together with N.                                                         

EXAMPLE 37

The reaction was carried out in a manner as described in Example 25,except that, from the top of the reaction tube, a starting gas mixturecomprising 18% by volume of cyclohexene, 14% by volume of methylnitrite, 14% by volume of oxygen, 15% by volume of nitrogen monoxide and39% by volume of nitrogen was fed at a rate of 20.4 l/hr and liquidmethanol was fed at a rate of 9 ml/hr (space velocity=1690/hr) and thereaction temperature was changed to 95° C.

As a result, 1,1-dimethoxy cyclohexane was obtained, as an acetal, at aspace time yield of 16.4 g/l.Cat.hr.

EXAMPLE 38

The reaction was carried out in a manner as described in Example 25,except that, from the top of the reaction tube, a starting gas mixturecomprising 18% by volume of methyl acrylate, 18% by volume of oxygen,29% by volume of nitrogen monoxide and 35% by volume of nitrogen was fedat a rate of 16.6 l/hr, gaseous methyl nitrite was fed at a rate of 3l/hr and liquid methanol was fed at a rate of 9 ml/hr (spacevelocity=1640/hr) and the reaction temperature was changed to 85° C.

As a result, methyl 3,3-dimethoxy propionate was obtained at a spacetime yield of 130 g/l.Cat.hr.

EXAMPLE 39

The reaction was carried out in a manner as described in Example 25,except that, from the top of the reaction tube, a starting gas mixturecomprising 18% by volume of propylene, 14% by volume of methyl nitrite,14% by volume of oxygen, 15% by volume of nitrogen monoxide and 39% byvolume of nitrogen was fed at a rate of 20.4 l/hr and liquid methanolwas fed at a rate of 9 ml/hr (space velocity=1690/hr) and the reactiontemperature was changed to 97° C.

As a result, aceton di n-butylacetal was obtained, as an acetal, at aspace time yield of 75 g/l.Cat.hr.

EXAMPLE 40

The reaction was carried out in a manner as described in Example 25,except that, from the top of the reaction tube, a starting gas mixturecomprising 15% by volume of acrylonitrile, 15% by volume of ethylnitrite, 18% by volume of ethanol, 11% by volume of oxygen, 16% byvolume of nitrogen monoxide and 25% by volume of nitrogen was fed at arate of 48 l/hr (space velocity=3200/hr) and the reaction temperaturewas changed to 75° C.

As a result, cyanoacetoaldehyde diethylacetal was obtained, as anacetal, at a space time yield of 33 g/l.Cat.hr.

EXAMPLE 41

The reaction was carried out in a manner as described in Example 25,except that a starting gas mixture comprising 14% by volume of methylnitrite, 14% by volume of oxygen, 16% by volume of nitrogen monoxide and56% by volume of nitrogen was fed at a rate of 16.7 l/hr and a methanolsolution containing 60% by volume of 1,4-hexadiene was fed at a rate of25 ml/hr (space velocity=1690/hr).

As a result, 5,5-dimethoxy-2-hexene was obtained, as an acetal, at aspace time yield of 24 g/l.Cat.hr.

EXAMPLE 42

The reaction was carried out in a manner as described in Example 25,except that, from the top of the reaction tube, a gas mixture comprising5% by volume of oxygen and 95% by volume of nitrogen was fed at a rateof 17 l/hr and a n-butanol solution containing 18% by volume of 1-hexeneand 22% by volume n-butyl nitrite was fed at a rate of 50 ml/hr (spacevelocity=1950/hr) and the reaction temperature was changed to 114° C.

As a result, 2,2-dibutoxy hexane was obtained, as an acetal, at a spacetime yield of 35 g/l.Cat.hr.

EXAMPLE 43

The reaction was carried out in a manner as described in Example 25,except that a starting gas mixture comprising 17% by volume of ethanol,14% by volume of oxygen, 18% by volume of nitrogen monoxide, 14% byvolume of ethyl nitrite, and 35% by volume of nitrogen was fed at a rateof 15.2 l/hr and an ethanol solution containing 20% by volume of ethylcrotonate was fed at a rate of 40 ml/hr (space velocity=1950/hr) and thereaction temperature was changed to 125° C.

As a result, ethyl β, β-diethoxy n-butyrate was obtained, as an acetalat a space time yield of 10 g/l.Cat.hr.

EXAMPLE 44

140 ml of methanol, 10 ml of acrylonitrite and 0.1 g of PdCl₂ werecharged into a pressure resistant glass autoclave provided with anagitator and, then, the content of the autoclave was heated to atemperature of 64° C. The reaction was carried out, while a nitrogen gascontaining 23% by volume of methyl nitrite was introduced into theautoclave at a rate of 200 ml/min. The reaction pressure was maintainedat 1 kg/cm² G. The reaction was carried out for 60 min. and, then, thereaction product was cooled. The results are shown in Table 6 below.

EXAMPLES 45 AND 46

Reactions were carried out in a manner as described in Example 44,except that the reaction conditions shown in Table 6 were used. Theresults are also shown in Table 6 below.

                  TABLE 6                                                         ______________________________________                                                        Example                                                                       44      45      46                                            ______________________________________                                        Reaction                                                                              Methanol (ml) 140       140   130                                     Conditions                                                                            Acrylonitrile (ml)                                                                          10        10    20                                              PdCl.sub.2 (g)                                                                              0.1       0.1   0.1                                             Temp. (°C.)                                                                          63-64     90    90                                              Press. (kg/cmG)                                                                             1         3     3                                               Period (hr)   1         1     1                                               Methyl nitrite (%)                                                                          23        24    23                                              Flow rate (ml/min.)                                                                         200       200   600                                     Result  Cyanoacetaldehyde                                                             Dimethyl Acetal                                                                             60.4      60.0  137.4                                   ______________________________________                                    

We claim:
 1. A process for producing an acetal comprising the stepsof:introducing an olefin, an alcohol, and an ester of nitrous acid intoa reaction system; and contacting, in a vapor phase, the olefin, thealcohol, and the ester of nitrous acid in the presence of at least onecomponent selected from the group consisting of platinum group metalsand the salts thereof and an iron compound, provided that a halide ispresent in addition to the iron compound if the iron compound is not ahalide of iron.
 2. The process as claimed in claim 1, wherein saidolefin is at least one compound selected from the group consisting ofolefins having 2 to 20 carbon atoms.
 3. The process as claimed in claim1, wherein said alcohol is at least one compound selected from the groupconsisting of alcohols having alkyl, cycloalkyl and aralkyl groups of 1to 12 carbon atoms.
 4. The process as claimed in claim 1, wherein saidester of nitrous acid is at least one compound selected from the groupconsisting of esters having 1 to 12 carbon atoms.
 5. The process asclaimed in claim 1, wherein said platinum group metals selected from arepalladium, platinum rhodium, rutenium, iridium and osmium.
 6. Theprocess as claimed in claim 1, wherein said salts of the platinum groupmetals selected from are chlorides, nitrates, sulfates, acetates,phosphates and complex salts.
 7. The process as claimed in claim 1,wherein the amount of the iron compound is 0.1 through 10 mol, in termsof an atomic number, based on the platinum group metal.
 8. The processas claimed in claim 1, wherein said process is carried out at atemperature of 50° through 200° C.
 9. The process as claimed in claim 1,wherein said process is carried out under a pressure of an atmosphericpressure through 20 kg/cm² G.
 10. The process as claimed in claim 1,wherein the ratio of the olefin, the alcohol and the ester of nitrousacid is 5 through 25% by volume, 5 through 25% by volume and 1 through30% by volume, respectively.